Related Stories

Development of an "artificial nose" is a step closer after US scientists reported finding a way to mass-produce smell receptors in a laboratory.

In a paper appearing online in Proceedings of the National Academy of Sciences, senior author Dr Shuguang Zhang says artificial noses could replace dogs that sniff out drugs and explosives, and could have numerous medical applications including identifying diseases that have distinct odours.

The olfactory receptors that bind to odour molecules are membrane proteins, which span the cell surface.

Since cell membranes are composed of a bi-layer of fatty lipid molecules, the receptor proteins are highly hydrophobic (water-fearing).

When such proteins are removed from the cell and placed in water-based solutions, they clump up and lose their structure, says Dr Liselotte Kaiser, lead author of the PNAS paper.

That makes it very difficult to isolate the proteins in quantities large enough to study them in detail.

Kaiser and others spent several years developing a method to isolate and purify the proteins by performing each step in a hydrophobic detergent solution, which allows the proteins to maintain their structure and function.

The technique reported this week in PNAS involves a cell-free synthesis using commercially available wheat germ extract to produce a particular receptor, then isolating the protein through several purification steps.

The method can rapidly produce large amounts of protein, enough to start structural and functional studies.

The team has also demonstrated a similar method that uses engineered mammalian cells to produce the receptors.

That method, reported in PLoS One in August, takes more time and labor than the cell-free approach, but could have advantages in that the receptor is processed more naturally.